Electrostatic discharge typically occurs when bodies at different electrical potentials are brought toward each other. The distance between the two bodies at which the discharge occurs is variable, depending upon a number of factors, such as the potential difference between the two bodies, the materials of which the bodies are formed, and the conductivity of the medium between them. It is not uncommon, under various circumstances, for the potential difference to be as great as about twenty-five thousand volts. However, because the amount of current that flows from one body to the next during such a discharge is typically extremely low, an electrostatic discharge is usually not harmful to a person.
However, an electrostatic discharge of even a much lower voltage difference can be extremely damaging to an integrated circuit, despite the low current flow. Because the structures of which an integrated circuit is formed are so small, an electrostatic discharge through an integrated circuit, which is typically designed to operate at about five volts, can easily physically damage the integrated circuit. Such damage can make the integrated circuit either unreliable or wholly inoperable. Thus, the reduction of the propensity for electrostatic discharge through an integrated circuit is an important goal in the microelectronics industry.
One situation where electrostatic discharge is a problem is where there is an electrically conductive contact that is open, or in other words, is not used, such as not being electrically connected to another element. Such a situation can occur, for example, when a standardized package substrate is used for mounting a variety of different integrated circuit designs. By using a single package substrate design for many different integrated circuit designs, the number of package substrate designs can be reduced, which yields various cost savings.
Because it is desirable to use just a single standardized package substrate design for a variety of different integrated circuit designs, the package substrate is fabricated to have electrically conductive contacts at all positions required by all of the different integrated circuit designs. However, not all of the different integrated circuit designs have electrically conductive contacts in the same positions. Thus, when a given integrated circuit is mounted on the standardized package substrate, there are typically many contacts on the package substrate that are left without any electrical connection to the integrated circuit.
These unused electrical connections on the package substrate often act as tiny antennas or lightening rods, and tend to either accumulate charge or serve as points for electrostatic discharge. As mentioned above, such electrostatic discharge tends to damage the packaged integrated circuit, or other elements of the circuit.
What is needed, therefore, is a system for reducing the occurrence of electrostatic discharge through a package substrate, such as into an integrated circuit.